Method of making a magnetoresistive read transducer having hard magnetic bias

ABSTRACT

A magnetoresistive (MR) read transducer having passive end regions separated by a central active region in which an MR layer is formed which extends over substantially only the central active region and in which a hard magnetic layer is formed in each end region. The hard magnetic layers form an abutting junction having electrical and magnetic continuity with the MR layer to produce a longitudinal bias in the MR sensor. The transducer is produced by a method in which the same stencil defines the extent of both the MR layer and the hard magnetic layers so that the abutting junctions are formed easily and reliably.

RELATED APPLICATIONS

This application is a division of application Ser. No. 07/419,246, filedon Oct. 10, 1989, in the name of M. T. Krounbi, et al., now U.S. Pat.No. 5,018,037.

BACKGROUND OF THE INVENTION

This invention relates to thin film magnetic heads, and, moreparticularly to a magnetic head having a magnetoresistive readtransducer.

The use of a magnetoresistive (MR) sensor to sense magnetically recordeddata has been known for many years. It has also been known that bothlongitudinal and transverse bias must be provided to eliminateBarkhausen noise and to maintain the sensor in its most linear operatingrange. Commonly assigned U.S. Pat. No. 4,024,489 describes an MR sensorin which a hard magnetic bias layer is used. In this sensor both the MRlayer and the hard magnetic bias layer extend across the entire sensorto produce a transverse bias.

Commonly assigned U.S. Pat. No. 3,840,898 discloses an MR sensor inwhich a transverse bias is produced In the embodiment shown in FIGS. 4and 5 a magnetoresistive stripe such as NiFe is treated in edge regionsto produce a hard magnetic state. However the edge regions are arrangedparallel to the direction of sense current and run along the entirestripe to produce a transverse bias and would not produce longitudinalbias.

It has become increasingly difficult to produce MR read transducers inthe small size needed to read the data recorded on ever decreasing trackwidths at ever increasing recording density. One solution proposed tomeet these requirements is described in commonly assigned U.S. Pat. No.4,663,685 in which transverse bias is produced in only a central activeregion of the sensor and longitudinal bias is produced in the inactiveend regions by means of exchange coupling between the part of theferromagnetic MR layer which extends into the end regions andantiferromagnetic layers which extend over only the end region. U.S.Pat. No. 4,639,806 shows an MR sensor which has longitudinal biasproduced by exchange coupling between the MR layer and hard magneticlayers in the end regions only.

These sensors have been shown to meet the present requirements. However,to meet future design requirements, the dimensional accuracy requiredseverely limits the ability to build these structures in processes thatare both economical and sufficiently accurate.

None of the known prior art references disclose an MR sensor in whichthe MR layer extends over substantially only the central active regionand a hard magnetic bias layer is provided in each end region whichforms an abutting junction with the MR layer to produce longitudinalbias in the MR sensor.

SUMMARY OF THE INVENTION

It is therefore the principal object of this invention to provide amagnetoresistive (MR) read transducer in which the MR layer extends oversubstantially only the central active region and a hard magnetic biaslayer is provided in each end region which forms an abutting junctionwith the MR layer to produce a longitudinal bias in the MR sensor.

In accordance with the present invention, the MR read transducercomprises an MR sensor having passive end regions separated by a centralactive region. A thin MR layer of ferromagnetic is formed which extendsover substantially only the central active region A first and secondfilm of hard magnetic material is formed extending over substantiallyonly one of the passive end regions and forming an abutting junctionhaving electrical and magnetic continuity with one end of the MR layerto produce a longitudinal bias in the MR sensor.

The preferred method for making the MR read transducer comprises thesteps of depositing a thin MR layer of ferromagnetic material over atleast the central active region of the transducer, producing a stencilcovering the central active region of the transducer, and etching awaythe part of the MR material not covered by the stencil. A film of hardmagnetic material is then deposited over regions of the transducer notcovered by the stencil to produce the passive end regions of thetransducer with the hard magnetic material forming an abutting junctionwith one end of the Mr material so that a longitudinal bias is producedin each of the passive end regions of the transducer.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention as illustrated inthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an end view of a prior art MR read transducer in whichlongitudinal bias is provided in the end regions only of the MR readtransducer.

FIG. 2 is a conceptual end view of an MR read transducer embodying thepresent invention.

FIG. 3 a-d is a diagram showing a specific embodiment of a process forfabricating a contiguous junction according to the present invention.

FIG. 4 is an exploded diagram showing in greater detail the formation ofthe contiguous junction according to a specific embodiment of thepresent invention.

FIG. 5 is an end view of a specific embodiment of an MR read transducerproduced in accordance with the process illustrated in FIGS. 3 and 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1 of the drawings, a prior art MR read transducer ofthe type described and claimed in commonly assigned U.S. Pat. No.4,663,685 comprises an MR layer 11 which extends over the entiretransducer 10'. An exchange bias layer 12 extends over the end regions14 only to produce a longitudinal bias field and a soft magnetic filmlayer 15, separated from the MR layer 11 by a thin non-magnetic spacerlayer 13, produces a transverse bias field in at least part of thecentral active region 16. The read signal is sensed over the centralactive region 16 which is defined in this embodiment by the spacingbetween conductors 18 and 20.

A conceptual view of an MR read transducer according to the presentinvention is shown in FIG. 2. The MR read transducer comprises an MRlayer 22 which extends over substantially only the central active region24 and a hard magnetic bias layer 26 in each end region 28 which formsan abutting junction 30 with the MR layer 22 to produce longitudinalbias in the MR read transducer 10. This embodiment does not requireadditional side-reading suppression components. Instead, the hardmagnetic bias layer 26 in each end region 28 need only provide forelectrical and magnetic continuity to the MR layer 22. The hard magneticbias layer 26 can be provided with a single layer of metallurgy such asCo Cr, Co Pt or Co Cr Pt, for example, although the use of under-and/orovercoats such as W or Au may be desirable. The thickness of a hardmagnetic layer is chosen so as to provide the desired amount of biasflux. As known to those skilled in the art, transverse bias is alsorequired in the central active region 24, and this bias can be providedby soft film bias, shunt bias, barber pole bias configuration, or anyother compatible transverse bias techniques. However, the transversebias structure has not been shown in the conceptual view of FIG. 2.

A specific embodiment of a process for fabricating a suitable junctionbetween the MR layer 22 and the hard magnetic bias layer 26 is shown inFIG. 3 a-d. The process comprises the steps of depositing, upon asuitable substrate 21 a film of MR material such as NiFe, for example,over the length of the sensor. In the embodiment shown, a transversebias structure comprising a soft magnetic film 23 and non-magneticspacer, layer 25 are deposited on substrate 21 prior to deposition ofthe MR layer 22. The process then continues by depositing a film of asuitable material such as photoresist, and patterning the photoresistmaterial to form a stencil 32 (FIG. 3a). Stencil 32 is used to defineeach edge of the MR layer 22 as the film of MR material 22 as well asthe spacer layer 25 and the soft magnetic film 23 are subjected to asubtractive process such as sputter etching, ion milling or chemicaletching to produce an MR trilayer structure 27 (FIG. 3b). The materialfor the hard magnetic bias layers 26 is then deposited as stencil 32again defines edges of the bias layers 26 (FIG. 3c). Using the samestencil 32, a conductor layer is deposited to produce conductor leads 29and 31. If desired, conductor leads 29 and 31 can be deposited in alater step if the conductor leads 29 and 31 are not coextensive with thehard bias layer 26. Note that a quantity of hard magnetic material andconductive material is also deposited on top of stencil 32. However thisquantity of material is removed, along with stencil 32 in a lift-offprocess (FIG. 3d) to produce a sensor having hard magnetic bias layers26 in the end regions only, each having a contiguous junction with theMR trilayer structure 27 which extends over only the central activeregion 24.

Although a square butted junction between the MR layer 22 and the hardmagnetic bias layer 26 is shown conceptually in FIGS. 2 and 3, thepreferred embodiment comprises a junction in which the topography iswell controllable so that the junction can be produced easily andreliably.

FIG. 4 shows in greater detail the formation of the contiguous junctionaccording to an embodiment of the present invention. In this case thestencil 32 comprises a bi-layer resist formed by a thin underlayer 33and a thick imaging layer 34. One exposure and one develop step definesthe edge profile of the resist. An undercut is created by dissolution ofthe underlayer 33 in a suitable developer with the undercut distancedetermined by the develop time.

The unmasked areas of the layer of MR material 35 are then removed bythe use of a unidirectional process such as ion milling, for example Theangle of incidence Φ is controlled by suitably tilting the substraterelative to the incident beam. In addition, circular symmetry isobtained by rotating the substrate so that any given point sees theincident beam rotate conically about the azimuth angle θ except near thestencil 32 whose edge shadows the film 35 during some segment ofsubstrate revolution. As shown in FIG. 4, for an azimuth angle of 0degrees, there is exposure of the film 35 to point C and the exposurelimit point moves progressively to the left until at an azimuth angle of180 degrees the exposure limit point is moved to point a. The combinedmilling for this embodiment produces a curved taper 36 as a result ofthe removal during the milling process of the part 37 of the film shownin dashed lines.

The hard magnetic bias layer 38 is then deposited, by sputtering, forexample, during a similar orientation and rotation of the substrate toproduce a deposition profile such as that shown in dashed lines 39. Thecombined junction profile resulting from the deposition of bias layer 38is shown in full line. Although the layer of MR material 35 is shown asa single layer in FIG. 4, it will be recognized that the MR element maycomprise other layers, such as transverse bias layers, for example.

This junction profile comprises two overlapping tapers The taper profileis determined by the height of the stencil 32 and the selected angle ofincidence Φ. In a specific embodiment the stencil thickness was about 1μm and the angle of incidence Φ was in the range of 70 to 80 degrees.This selected combination produced a taper length of about five timesthe thickness of the sensor For electrical reliability the junctionshould be long, however, for magnetic reliability the junction should beshort. For a particular application, junction lengths within the rangeof 3 to 5 times the sensor thickness were shown to be suitable.

The magnetoresistive read transducer made by the above-described methodis shown in FIG. 5 which shows the edge view of the sensor, i.e., thesurface which is in close proximity to the magnetic recording mediumfrom which previously recorded magnetic data is to be read. Thetransducer comprises an MR element 42 which extends over the centralactive region 44 of the transducer, and hard magnetic bias layers 46which form an abutting junction 48 with the MR element 42. The hardmagnetic bias layers 46 extend over the end regions 50 of the transducerso that a longitudinal bias can be produced in the end regions 50 onlyof the transducer.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various other changes in the form anddetails may be made therein without departing from the spirit and scopeof the invention.

Having thus described our invention, what we claim as new, and desire tosecure by Letters Patent is:
 1. A method for making a magnetoresistiveread transducer having passive end regions separated by a central activeregion comprising the steps of:depositing a thin magnetoresistive layerof ferromagnetic material over at least the central active ion of saidtransducer; producing a stencil covering the central active region ofsaid transducer; etching away the part of said magnetoresistive materialnot covered by said stencil to form the central active region of saidtransducer; depositing a film of hard magnetic material over regions ofsaid transducer not covered by said stencil to produce the passive endregions of said transducer, said hard magnetic material in said endregions forming an abutting junction with one end of said layer ofmagnetoresistive material so that a longitudinal bias is produced ineach of said passive end regions of said transducer.
 2. The method formaking a magnetoresistive read transducer according to claim 1 whereinsaid etching step comprises the use of a directional etching method. 3.The method for making a magnetoresistive read transducer according toclaim 2 wherein said directional etching method comprises ion beammilling.
 4. The method for making a magnetoresistive read transduceraccording to claim 2 wherein said directional etching method is carriedout at an angle to said transducer.
 5. The method for making amagnetoresistive read transducer according to claim 4 wherein said angleis within the range of 70 to 80 degrees.
 6. The method for making amagnetoresistive read transducer according to claim 4 wherein saidtransducer is rotated in a plane normal to said angle during saidetching step.
 7. The method for making a magnetoresistive readtransducer according to claim 5 wherein said stencil comprises aphotoresist material.
 8. The method for making a magnetoresistive readtransducer according to claim 7 wherein said photoresist materialcomprises a thin underlayer and a thick imaging layer.
 9. The method formaking a magnetoresistive read transducer according to claim 8 whereinsaid thin underlayer is undercut.
 10. The method for making amagnetoresistive read transducer according to claim 1 additionallycomprising the step of depositing means for producing a transverse biasin at least a part of said central active region.
 11. The method formaking a magnetoresistive read transducer according to claim 10 whereinsaid means for producing a transverse bias comprises a soft magneticfilm spaced from said magnetoresistive layer.